This invention relates to a process for producing 1,5-dinitroanthraquinone and, in particular, to a process for separating 1,5-dinitroanthraquinone of a high purity from a mixture containing various dinitroanthraquinone isomers prepared from anthraqinone by nitrating the same with a mixed acid (a mixture of nitric acid and sulfuric acid).
Dinitroanthraquinones have been used widely, in general, as an intermediates for the production of dyes or the like and, among all, 1,5-dinitroanthraquinone is important as an intermediate for blue color dyes of a high fastness to sublimation. 1,5-dinitroanthraquinone is generally produced by nitrating anthraquinone with a mixed acid but the 1,5-dinitroanthraquinone thus prepared contains, in most cases, 1,8-dinitroanthraquinone, 1,6-dinitroanthraquinone, 2,6-dinitroanthraquinone and the like, that is, it is obtained as a mixture of various isomers.
Isolation of pure 1,5-dinitroanthraquinone from the above isomer mixture has heretofore required a complicated process, for example, heating the mixture together with 100% by weight sulfuric acid to isolate less soluble 1,5-dinitroanthraquinone from other isomers and then further recrystallizing the same from an appropriate solvent.